A couple of weeks ago, my car wouldn't start after sitting in a parking lot in cold weather for a couple of hours. (I park it in an unheated garage at home). I had it towed to a garage and after sitting in their garage overnight, it started for them. They checked it over and found that it needs a tuneup (plugs, air filter & fuel filter). They also said it may have had a little gasline freeze. I put heet in it and filled the tank. It ran fine for the next several days. Then my husband was on vacation for over a week and the sable sat in the unheated garage for over a week without being ran while we used our SUV. The wind chill temps got down to about -20 to -30 during this time. I went to use the car today and it would not start. Ironically, the temp got to about 20 above zero today. I hooked up portable heaters in the garage to warm the car, but it didn't help. My husband came home from work and replaced the fuel filter. The car started right up and then started running very rough (idling up and down) and then died. Now it won't start again and the check engine light is on. My brother suggested it might be a weak fuel pump or an oxygen sensor. Are these possibilities? How would I go about determining this without having it towed in and pay for a diagnostic again? Could the plugs being bad cause the car to react this way? (Husband is going to replace the plugs tomorrow night). Any info or advice would be greatly appreciated.